A flat engine is an internal-combustion engine with multiple pistons that move in a horizontal plane. In FIG. 1, one such engine, an opposed-piston, opposed-cylinder (OPOC) engine 10, is shown isometrically and partially exploded. An intake piston 12 and an exhaust piston 14 reciprocate in a first cylinder 26 and an intake piston 22 and an exhaust piston 24 reciprocate in a second cylinder 28. Exhaust piston 24 and intake piston 12 couple to a journal (not visible) of crankshaft 20 via pushrods 16. Only half of cylinders 26 and 28 are shown exploded from pistons 12, 14, 22, and 24 so that the features can be more easily viewed. Cylinders 26 and 28 each have intake ports 30 and exhaust ports 32 Intake piston 22 and exhaust piston 14 couple to two journals (not visible) of crankshaft 20 via pullrods 18, with each of intake piston 22 and exhaust piston 14 having two pullrods 18. A well-known issue with flat engines is in controlling oil, i.e., returning it to the sump to avoid oil pooling in the outer extremities due to a lack of natural gravity draining effect. Also, with a flat engine layout, if the engine is tipped, e.g., parked at an angle, oil may flow from the sump toward the extremity that is dropped lower. If the angle is extreme, the level of oil could be such that the engine becomes hydraulically locked. If the engine is not operating while at the extreme angle, the engine would not start. If the engine is operating, the engine could be damaged.